The clinical trial is the vehicle by which basic science and applications to human disease merge. Sufficient enrollment is necessary for the successful conduct of any clinical trial. Results from recent trials indicate that enrollment is often inadequate or delayed, jeopardizing the validity of the findings. These concerns are salient as the Cardiac Arrhythmia Suppression Trial (CAST), a major test of antiarrhythmic therapy on mortality among post- myocardial infarct patients, will be initiated during the Summer of 1987. To assess the potential problem of patient nonenrollment, the CAST Experimental Assessment of Suppressor Enrollment will be conducted primarily to determine which factors contribute to patient decisions to enroll or refuse to enroll in the CAST trial. This research project will be conducted at ten (10) participating CAST Centers. The research project will be coordinated by the clinical research staff within the Brown University CAST Center, in cooperation with the Clinical Trials Branch of The National Heart, Lung and Blood Institute. CAST design issues with implications for enrollment are discussed. Based on reviews of relevant enrollment and compliance literatures, both patient characteristics (i.e., demographic, patient knowledge, psychosocial, clinical, and patient perception/patient satisfaction with care factors) and recruitment processes (i.e., physician recruitment, patient-staff interaction, physician characteristics, and facility characteristics) will be assessed. A discriminant analysis will be used in the attempt to differentiate 800 eligible patients, 400 who do and 400 do not enroll in the trial. Of secondary interest is to determine what factors contribute to the decision of enrolled patients to withdraw from the trial prior to randomization. The information gathered in this study of CAST enrollment may have significant utility toward the success of the CAST and/or future trials by identifying factors that may be modified to enhance initial enrollment and participation for the duration of the trial.